spang in the center of the Pont-Neuf

Any chance it's a typo, tsuwm? The meaning would be the same if the author intended "sprang".

re "spang springs entire new upon me": Could be it sprang entire new on the author himself.

Upon further investigation, it is more likely that "spang", which is defined in Merriam-Webster thus "Etymology: Scots spang to leap, cast, bang", evolved into "sprang", for they both mean pretty much the same thing, especially in the context in which you encountered the word, tsuwm.

Typos sping eternal. [They are not just a phenomenon of our own time. It reminds me of the aphorism: "Antiquity cannot privilege an error, nor novelty prejudice a truth."]